The success of CPR is vastly overrated by patients, a new study suggests.

Not only does the general public consider CPR more effective than it really is, they tend to discount the negative effect it can have, the researchers said.

Doctors should discuss CPR's success rate, benefits and risks with patients and their loved ones, the study authors suggested. CPR is an emergency procedure for someone whose heart has stopped or who is no longer breathing.

Emergency doctors often talk to patients or their families about end-of-life care and the process of resuscitation. Patient and family expectations for CPR can affect the medical care that's given, according to Dr. Norkamari Shakira Bandolin, of the University of California, Davis, and colleagues.

In earlier studies, patients have pegged CPR survival rates at between 19% and 75%. But the real rate of survival is about 12% for cardiac arrests that occur outside hospitals and between 24% and 40% for those that happen in the hospital, according to the report published online July 13 in the Emergency Medicine Journal.

For the new study, Bandolin's team surveyed 500 emergency department patients and their companions.

Fifty-three percent said they had done or witnessed CPR, and 64% had taken a CPR course. Ninety-five percent said their main source of CPR information was television.

About half said the success rate of CPR topped 75%. And nine out of 10 said they wanted to receive CPR if it was needed.

But only 28% had discussed CPR with a doctor, the investigators noted in a journal news release.

"These findings should prompt emergency department physicians to initiate discussions about resuscitation with their patients while also providing them with key information to help facilitate informed decision-making," the researchers wrote.

The study authors said that discussion should focus "on true rates of survival and outcomes" and should not assume that a patient or companion with health care experience will have realistic expectations.